Alkaline cleaning treatments are employed in a variety of metal forming and coating processes. Satisfactory treatment of metals requires that any dirt and lubricants from the forming and coating operations be removed. This is particularly necessary in the production of aluminum where cleaning operations to remove oil and debris precede conversion coatings or other coating operations.
Alkaline and acid cleaners have found wide use in the cleaning of aluminum. Acid etching and cleaning with, for example, hydrofluoric acid gives good results producing clean, mirror bright surfaces. However, the use of acids for cleaning presents safety and effluent disposal problems. Acidic solutions will also attack the cleaning equipment, that is, the tank, pumps and flow lines. This necessitates that this equipment be made of stainless steel. For these reasons, alkaline cleaning and etching processes are favored in the aluminum processing industry.
Many alkaline cleaners are based on phosphate compounds. These phosphates aid in detergency, sequestration and stabilization. However, with the advent of growing environmental concerns about phosphates, their use is being reconsidered in cleaning and etching formulations.
With prior art cleaning solutions, the accumulation of oils in the bath presents a three fold problem. First, the presence of oils makes metal cleaning more difficult as the capacity of surfactants to emulsify oil from the metal becomes limited. Second, in alkaline baths, the oils may saponify and thereby contribute to foaming. Lastly, subsequent treatment of the effluent must separate out the emulsified oils prior to discharge. Higher treatment levels of surfactants are often used to remedy the problems of insufficient cleaning in the presence of oils. This may result in an increase in foam generation and difficulties in breaking the oil/water emulsion prior to the discharge of the effluent.
Virtually any material which is capable of removing oil contamination from an aluminum surface will possibly remove some aluminum. This circumstance, coupled with the economic necessity for recycling the cleaner bath, causes ever increasing amounts of aluminum in the bath. At some point, insoluble aluminum compounds will tend to drop out of the cleaning solution in the form of sludge. Such sludge can cause cleaning problems if it redeposits as a film or smut on the aluminum that has just been cleaned.
The inventive composition and methods of using avoid the problems associated with prior processes. The inventive composition offers good cleaning of aluminum, and generates a shiny surface while providing low etching of aluminum and avoiding the use of phosphates in the cleaning process.